1. Field of the Invention
The present invention relates to a solenoid valve, and more particularly to a solenoid valve including a sleeve which has an internal space that is formed with an input port, an output port and a drain port, a spool which is an axial member inserted into the internal space and which is capable of the communications and cuts-off among the individual ports, through the axial movements thereof, and a solenoid portion which axially moves the spool.
2. Description of Related Art
Heretofore, as a solenoid valve of this sort, there has been proposed one including a sleeve which has a cylindrical valve chest that is formed with an input port, an output port, a drain port and a feedback port as several sorts of ports allowing an oil to flow in and out, a spool which is an axial member inserted into the valve chest and which has a plurality of cylindrical lands each having an outside diameter substantially equal to an inside diameter of the valve chest, and a cylindrical communication portion having an outside diameter smaller than an outside diameter of each land and communicating the individual ports, and a solenoid which axially moves the spool (refer to, for example, JP-A-2004-176895 (Patent Document 1)). In this solenoid valve, notches are formed in the end edges of the lands, and it is described that part of the working oil inputted from the input port is drained from the drain port through the notches, whereby the pressure fluctuation of the working oil can be suppressed.
With the above solenoid valve, the working oil is drained from the drain port through the notches, whereby the pressure fluctuation of the working oil is suppressed from becoming excessive, and a smooth pressure regulation control can be realized, but a flow rate which is outputted from the output port decreases in correspondence with the drainage, and an output pressure lowers. For attaining a required output oil pressure, therefore, it becomes necessary, for example, to raise the r.p.m. of a pump which pressure-feeds the working oil, and energy consumption increases.